docs: add Related tools link + HalfToEdge build note

handwriting/readme.md

@@ -103,3 +103,24 @@ The colour calibration is closed loop, so in principal requires access to the or
  5. You can now use the `handwriting/calibrate_printer/apply_cm.py` command line tool to convert original image files - if run with `-h` it will tell you how to use it, but it's simply `./apply_cm.py input_file.png file_saved_above.colour_map output_file.png` Note there is also `apply_cm_dir.py`, which can be used to process an entire directory at once.
  6. The file generated above is what you now send to the printer - it will have distorted the colours to make the printer do something closer to the right thing.
 
+## Related tools
+
+- **Handwriting formatting pipeline (companion toolkit)** — line-layout / print formatting using a marker glyph, yellow-line cleanup + deskew, splicer/splitter, and limited Unicode↔ASCII mapping with runnable examples.  
+  Repo: https://github.com/Martonveghcode/Handwriting-formatting-pipeline
+
+---
+
+### Build note (Ubuntu 20.04 / Python 2.7): `HalfToEdge` symbol
+
+If you see an error like:ImportError: ... line_graph_c.so: undefined symbol: HalfToEdge
+
+
+Cause: `HalfToEdge` is defined inline in `line_graph_c.h` and also defined again in `line_graph_c.c`.  
+On some compilers/linkers this can cause a symbol issue when building `line_graph_c.so`.
+
+**Workaround tested:** keep only the header inline version.  
+Removing the duplicate in `line_graph_c.c` resolved the issue on Ubuntu 20.04 / Python 2.7.
+
+
+
+